1. Field of the invention
The present invention relates to photovoltaic devices and particularly to a photovoltaic device having a high photoelectric conversion efficiency, which can be manufactured at a low cost.
2. Description of the Prior Art
U.S. Pat. No. 4,281,208, for example, discloses a photovoltaic device having a laminated structure in which a light incident electrode, an amorphous semiconductor film including a photoactive layer for receiving light and generating carriers, and a back plate electrode are placed one upon another in this order on a transparent substrate of glass or the like. Such a photovoltaic device using an amorphous semiconductor film for a photoactive layer has a reduced manufacturing cost for a unit quantity of generated energy compared with a photovoltaic device using a single crystal wafer; however, it has a low photoelectric conversion efficiency.
In a photovoltaic device described by S. Nakano et al. in Technical Digest of International PVSEC-1 (1984), pp. 583-586, an amorphous semiconductor film including a photoactive layer is formed on a light acceptance electrode having a rough surface texture, whereby incident light is confined within the semiconductor film, which makes it possible to improve the photoelectric conversion efficiency.
In general, a light acceptance electrode comprises a single layer or multiple layers of transparent conductive oxide (TCO) such as tin indium oxide or tin oxide. Such a TCO electrode is formed on a transparent substrate of glass or the like, mainly by a thermal CVD process. On that occasion, the substrate needs to be maintained at a high temperature of about 500.degree. C. in order to ensure a sufficient transparency for the TCO electrode and accordingly a large quantity of electric energy is required. As a result, the manufacturing cost of the TCO electrode is higher than the manufacturing cost for other films, which makes it difficult to reduce the manufacturing cost per a unit quantity of generated energy in a photovoltaic device.